ARTHUR STANLEY EDDINGTON
Eddington was a brilliant scholar. His ;rst position after graduating from Cambridge University (1906) was that of chief assistant at the Royal Observatory in Greenwich, where he excelled in practical astronomy. In 19B he was appointed Plumian Professor of Astronomy at Cambridge and a year later made director of the observatory.
In the years following, his intuitive insight, bold imagination, and mastery of mathematics led him to important discoveries over a wide range of problems. Eddington was the first to model the interior of a star under radiative equilibrium, pointing out that the condition for stellar equilibrium involved three forces: gravity, gas pressure, and radiation pressure. Recognizing the importance of ionization in stellar interiors, he boldly assumed that, because of the high ionization of the internal gases, the perfect-gas condition prevailed within the interiors of the stars, except for the white dwarfs. This hypothesis was later accepted. He demonstrated that energy could be transported by radiation as well as by convection and that the centers of stars must be at very high temperatures-in the millions of degrees. An extremely important result that emerged from his research was his theoretical formulation of the mass-luminosity relation, verified later by stellar data.
Eddington suspected that the chief source of stellar energy was subatomic and that hydrogen played a dominant role in supplying this energy. Later, in 1938 and 1939, Bethe introduced the theory for the fusion of hydrogen into helium, which clarified the picture of stellar energy generation and substantiated Eddington's speculations.
In 1919 Eddington organized a solar-eclipse expedition to Brazil to photograph the stars in the neighborhood of the eclipsed sun. This was to test whether or not a beam of starlight would bend when going by the sun, as predicted by Einstein's general theory of relativity. Although difficult to measure, the observed deflection was in rough agreement with Einstein's predicted val ue - the fi rst observational test of relativity theory .
